This invention relates to a circuit configuration and method for maintaining or improving the control function for a traction slip control system with brake and/or engine management for automotive vehicles when a smaller spare wheel has been mounted as a driven wheel instead of a normal size wheel. In the present invention, the rotating speed of the driven wheels is compared with the vehicle speed or with a corresponding measurement parameter for the purpose of detecting the traction slip. A correction factor is obtained from the rotating speeds measured with stable rotational behavior of the wheels. Traction slip control is triggered when wheel slip exceeds a predetermined limit value, namely the so-called slip threshold.
There are known circuit configurations for traction slip control systems. The information needed for control is obtained by means of wheel sensors, important information being developed from the comparison of the rotational behavior of the individual wheels and by distinguishing between the driven wheels and the non-driven wheels.
Replacing a normal wheel by an emergency wheel of the type in current use today, the dimensions of which often differ considerably from those of normal wheels, can lead to faulty information for traction slip control.
What, above all, is critical is the replacement of a driven wheel by an emergency wheel, the diameter of which is smaller than the diameter of the normal wheel. The traction slip control system identifies the higher rotating speed of the emergency wheel, caused by the smaller diameter, as "traction slip", with the control system responding and metering braking pressure into the wheel brake of the emergency wheel. This metering-in of braking pressure may completely prevent the car from starting in some situations such as in case of different right/left friction coefficients when the emergency wheel is located on the higher friction coefficient side. Up to now, in order to avoid this situation, it was necessary to turn off the traction slip control when an emergency wheel has been mounted.